The spinal cord ends at the level of the first or second lumbar vertebrae (L1 / L2) as a cone-shaped termination called the conus medullaris (medullary cone). It consists of the sacral and coccygeal spinal cord segments (S2 - Co1 segments).

A small and thin connective tissue strand arises from the tip of the medullary cone. It is known as the filum terminale, and it extends inferiorly from the medullary cone to the coccyx. The filum terminale stabilizes the distal aspect of the spinal cord and anchors it in place.

Distal to the medullary cone is the cauda equina, which occupies the lower third of the vertebral canal. The cauda equina is a bundle of the lower spinal nerve roots that arise from the lumbosacral enlargement and descends towards the coccyx.

It is formed by the second through fifth lumbar (L2 - L5), all the sacral (S1 - S5) and coccygeal (Co1) spinal nerve roots. These nerves provide nerve supply to the pelvic organs, perineum and the lower limbs. The name cauda equina derives from Latin, meaning “horse's tail” due to its resemblance to a horsetail.

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Conus medullaris, filum terminale and cauda equina